Gear drive cooling with oil sump submersed forced air cooling tubes

ABSTRACT

A high power industrial gear drive with a cooling system that improves upon the designs of shaft fan and electrical fan cooling systems for gear drives by effectively increasing the wetted surface area of the gear drive housing through the introduction of heat exchange tubes through the internal gear drive oil sump and providing cooling surfaces directly in the sump oil for convection from air flow created by the fans through the heat exchange tubes.

FIELD OF THE INVENTION

The invention relates to high power gear drives, and more particularly to high power gear drives with oil sump cooling systems.

BACKGROUND OF THE INVENTION

The power that an industrial gear drive can transmit is limited by mechanical and thermal ratings. The mechanical rating is based on the mechanical properties and design of internal components. Due to innovations in component designs, such as carburised and hardened gears and cleaner bearing steels, gear drives are becoming more torque dense as the components get smaller. The drives have the ability to transmit more torque for a given size, but in doing so they generate more heat.

The thermal rating is based on the ability of the gear drive to dissipate the generated heat and it must be higher than the actual application transmitted power. Because of the decrease in overall size of modern gear drives, these gear drives are not able to dissipate the heat generated by their mechanical rating and are therefore limited thermally. A gear drive is typically limited to operate at approximately 200 degrees Fahrenheit. This is because the sump oil for the gear drive loses its ability to adequately lubricate internal components due to the combination of an unacceptable decrease in viscosity and increase in oil oxidation rate at higher temperatures.

An oil sump cooling system may be incorporated in order to increase the thermal rating of modern gear drives. Such cooling systems have been of four general types. One general type is a mechanical shaft fan that is typically coupled to the input or first intermediate drive shafts of the gear drive. Another is an electric fan that is attached to the drive. A third is an internal heat exchanger comprising water-filled heat exchange tubes. The fourth is an external heat exchanger of the oil-to-air or oil-to-water type.

A major problem with shaft fan cooling is that it often does not dissipate enough heat and the drive shall be limited thermally. Electric fans offer better cooling than shaft fans, but they can also provide inadequate heat dissipation or the additional electronic connections are unwanted. External heat exchangers are expensive and take up ground space. They also need additional electric connections for their external blowers and might require water, depending on type.

Internal heat exchangers that comprise water-filled heat exchange tubes typically provide an increase in thermal rating over both fan methods, but installations might not have a water supply or the water is too expensive.

SUMMARY OF THE INVENTION

In the preferred embodiment, the invention comprises a gear drive with an air-cooled oil sump comprising: at least one heat exchange tube that passes through the sump of the gear drive and has an air inlet and an air outlet; a fan for pressurising ambient air; and a conduit for directing at least a portion of the pressurised air through the heat exchange tube to cool oil in the sump.

The invention thus comprises a high power industrial gear drive with a cooling system that improves upon the designs of shaft fan and electrical fan cooling systems for gear drives by effectively increasing the wetted surface area of the gear drive housing through the introduction of heat exchange tubes through the internal gear drive oil sump and providing cooling surfaces directly in the sump oil for convection from air flow created by the fans through the heat exchange tubes. It is also less expensive than gear drive cooling systems with external heat exchangers and it does not require water as a cooling media.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a gear drive with a cooling system according to a preferred embodiment of the invention that uses a motor-driven fan for cooling air circulation.

FIG. 2 is a side view of a gear drive with a cooling system according to a preferred embodiment of the invention that uses a motor-driven fan for cooling air circulation.

FIG. 3 is a side cut-away view of a gear drive with a cooling system according to a preferred embodiment of the invention that uses a motor-driven fan for cooling air circulation.

FIG. 4 is a top cut-away view of a gear drive with a cooling system according to a preferred embodiment of the invention that uses a motor-driven fan for cooling air circulation.

FIG. 5 is a partial side cut-away view of a gear drive with a cooling system according to an alternate embodiment of the invention that uses a drive shaft driven fan for cooling air circulation.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 4 show different views of the gear drive with a cooling system according to a preferred embodiment of the invention that uses a motor-driven fan for cooling air circulation. FIG. 1 is a top view, FIG. 2 is a side view, FIG. 3 is a top cut-away view that shows internal structure, and FIG. 4 is a side cut-away view that shows internal structure. Referring to FIGS. 1 through 4 together, a gear drive 2 has an internal oil sump 4 with oil level 6 within a housing 8 for the gear drive 2. At least one heat exchange tube 10 extends through the oil sump 4 and attaches to opposite sides of the housing 8. Two of the heat exchange tubes 10 are shown in FIGS. 3 and 4.

Each heat exchange tube 10 has an air inlet 12 and an air outlet 14 that are external to the housing 8. Preferably, each heat exchange tube 10 also has a plurality of cooling fins 16 to maximise heat transfer. The cooling fins 16 may be arranged on an external surface of each heat exchange tube 10, an internal surface of each heat exchange tube 10, or both. An air collector or scoop 18 is attached to each air inlet 12 to air that impinges on it through each air inlet 12. With a plurality of heat exchange tubes 10 the air scoop 18 preferably comprises a manifold so that a single air scoop 18 couples to the plurality of corresponding air inlets 12, as shown in FIG. 4.

A motor-driven fan 20 pressurises ambient air for cooling and has its exhaust coupled with an air duct or conduit 22 to the housing 8. Generally, the motor-driven fan 20 has an electric motor, but it may have another type of motor, such as pneumatic or hydraulic. The conduit 22 conveniently mounts the fan 20 to the housing 8. The conduit 22 directs at least a portion of the exhaust from the fan 20 to impinge upon the air scoop 18 to force the pressurised air through the heat exchange tubes 8 by way of their respective air inlets 12 and air outlets 14.

The invention as described above in connection with the preferred and alternate embodiments improves upon the designs of prior art shaft fan and electrical fan gear drive cooling systems by effectively increasing the wetted surface area of the housing through the introduction of heat exchange tubes in the sump and providing cooling surfaces directly in the sump oil for convection from the air flow created by the fans. It is also less expensive than external heat exchangers and it does not require water as a cooling media.

The pressurised air that passes through the heat exchange tubes 8 absorb heat from oil in the oil sump 4 by way of the contact surfaces of the heat exchange tubes 8 and their respective cooling fins 16. Air discharge ports 24 in the conduit 20 preferably direct the remainder of the pressurised air toward the perimeter of housing 8 to provide additional cooling of the gear drive 2.

FIG. 5 is a partial side cut-away view of a gear drive with a cooling system according to an alternate embodiment of the invention identical in all respects to the preferred embodiment of the invention described above in connection with FIGS. 1 through 4 except that uses a drive shaft driven fan for cooling air circulation. In this case, a shaft fan 26 coupled to a drive shaft 28 that protrudes from the housing 8 of the gear drive 2 pressurises ambient air for cooling and has its exhaust coupled with an air deflector or conduit 22 to the housing 8. The conduit 22 conveniently mounts the fan 20 to the housing 8. The conduit 22 directs at least a portion of the exhaust from the fan 20 to impinge upon the air scoop 18 to force the pressurised air through the heat exchange tubes 8 by way of their respective air inlets 12 and air outlets 14.

The pressurised air that passes through the heat exchange tubes 8 absorb heat from oil in the oil sump 4 by way of the contact surfaces of the heat exchange tubes 8 and their respective cooling fins 16. Air discharge ports 24 in the conduit 20 preferably direct the remainder of the pressurised air toward the perimeter of housing 8 to provide additional cooling of the gear drive 2.

Thus there has been described herein a high power industrial gear drive with a cooling system that improves upon the designs of shaft fan and electrical fan cooling systems for gear drives by effectively increasing the wetted surface area of the gear drive housing through the introduction of heat exchange tubes through the internal gear drive oil sump and providing cooling surfaces directly in the sump oil for convection from air flow created by the fans through the heat exchange tubes. It should be understood that the embodiments described above are only two illustrative implementations of the invention, that the various parts and arrangement thereof may be changed or substituted, and that the invention is only limited by the scope of the attached claims. 

1. A gear drive with an air-cooled oil sump comprising: at least one heat exchange tube that passes through the sump of the gear drive that has an air inlet and an air outlet; a fan for pressurising ambient air; and a conduit for directing at least a portion of the pressurised air through each heat exchange tube by way of its air inlet and air outlet to cool oil in the sump.
 2. The gear drive of claim 1, further comprising an air scoop for coupling pressurised air in the conduit to the air inlet of each heat exchange tube.
 3. The gear drive of claim 2, wherein each heat exchanger tube has a plurality of cooling fins immersed in the oil sump.
 4. The gear drive of claim 3, wherein the gear drive has a single one of the heat exchanger tubes.
 5. The gear drive of claim 3, wherein the gear drive has at least two of the heat exchanger tubes.
 6. The gear drive of claim 5, wherein the air scoop comprises a manifold for coupling pressurised air in the conduit to the air inlet to each of the heat exchanger tubes.
 7. The gear drive of claim 2, wherein the fan is coupled to a fan motor and the conduit comprises an air duct that shrouds the exhaust of the fan to impinge upon the air scoop.
 8. The gear drive of claim 7, wherein the gear drive has a single one of the heat exchanger tubes.
 9. The gear drive of claim 7, wherein the gear drive has at least two of the heat exchanger tubes.
 10. The gear drive of claim 9, wherein the air scoop comprises a manifold for coupling pressurised air in the conduit to the air inlet to each of the heat exchanger tubes.
 11. The gear drive of claim 2, wherein the fan is coupled to a drive shaft on the gear drive and the conduit comprises an air deflector that shrouds the exhaust of the fan to impinge upon the air scoop.
 12. The gear drive of claim 11, wherein each heat exchanger tube has a plurality of cooling fins immersed in the oil sump.
 13. The gear drive of claim 12, wherein the cooling fins are arranged along an external surface of each heat exchanger tube.
 14. The gear drive of claim 12, wherein the cooling fins are arranged along an internal surface of each heat exchanger tube.
 15. The gear drive of claim 12, wherein the cooling fins are arranged along the external and internal surfaces of each heat exchanger tube.
 16. The gear drive of claim 12, wherein the gear drive has a single one of the heat exchanger tubes.
 17. The gear drive of claim 12, wherein the gear drive has at least two of the heat exchanger tubes.
 18. The gear drive of claim 17, wherein the air scoop comprises a manifold for coupling pressurised air in the conduit to the air inlet to each of the heat exchanger tubes.
 19. A gear drive with an air-cooled oil sump comprising: at least one heat exchange tube that passes through the sump of the gear drive and has an air inlet and an air outlet; an air scoop coupled to the air inlet of each heat exchange tube; a motor-driven fan for exhausting pressurised ambient air; an air duct for directing at least a portion of the fan exhaust to impinge upon the air scoop and force the pressurised air through each heat exchange tube by way of its air inlet and air outlet to cool oil in the sump.
 20. The gear drive of claim 19, wherein each heat exchanger tube has a plurality of cooling fins immersed in the oil sump.
 21. The gear drive of claim 20, wherein the cooling fins are arranged along an external surface of each heat exchanger tube.
 22. The gear drive of claim 20, wherein the cooling fins are arranged along an internal surface of each heat exchanger tube.
 23. The gear drive of claim 12, wherein the cooling fins are arranged along the external and internal surfaces of each heat exchanger tube.
 24. The gear drive of claim 20, wherein the gear drive has a single one of the heat exchanger tubes.
 25. The gear drive of claim 20, wherein the gear drive has at least two of the heat exchanger tubes.
 26. The gear drive of claim 25, wherein the air scoop comprises a manifold for coupling pressurised air in the conduit to the air inlet to each of the heat exchanger tubes.
 27. A gear drive with an air-cooled oil sump comprising: at least one heat exchange tube that passes through the sump of the gear drive that has an air inlet and an air outlet; an air scoop coupled to the air inlet of each heat exchange tube; a fan coupled to a drive shaft on the gear drive for exhausting pressurised ambient air; an air deflector to direct at least a portion of the fan exhaust to impinge upon the air scoop and force the pressurised air through each heat exchange tube by way of its air inlet and air outlet to cool oil in the sump
 28. The gear drive of claim 27, wherein each heat exchanger tube has a plurality of cooling fins immersed in the oil sump.
 29. The gear drive of claim 28, wherein the cooling fins are arranged along an external surface of each heat exchanger tube.
 30. The gear drive of claim 28, wherein the cooling fins are arranged along an internal surface of each heat exchanger tube.
 31. The gear drive of claim 28, wherein the cooling fins are arranged along the external and internal surfaces of each heat exchanger tube.
 32. The gear drive of claim 28, wherein the gear drive has a single one of the heat exchanger tubes.
 33. The gear drive of claim 28, wherein the gear drive has at least two of the heat exchanger tubes.
 34. The gear drive of claim 33, wherein the air scoop comprises a manifold for coupling pressurised air in the conduit to the air inlet to each of the heat exchanger tubes. 